Noncovalent interactions of bovine alpha-lactalbumin with green tea polyphenol, epigalocatechin-3-gallate

Abstract

Bovine alpha-lactalbumin (ALA) is an important Ca-binding protein of milk. Epigallocatechin-3-gallate (EGCG) is the major and the most biologically active catechin of green tea, which has the highest binding affinity to whey proteins due to galloyl functional group. In this study experimental and computational methods were used to investigate noncovalent interactions of EGCG and ALA. Binding affinity of EGCG for ALA, determined by fluorescence quenching analysis, was in the range described for complexes of EGCG and other dietary proteins, and lower than affinity of some phenolic compounds to ALA. Based on circular dichroism and Fourier transform infrared spectroscopy spectra, binding of EGCG change ALA conformation inducing alpha-helix to beta-structures transition. The isothermal titration calorimetry results suggest that the binding of EGCG to ALA is enthalpically favorable. The docking analysis shows that EGCG binds in the hydrophobic pocket at the entrance of cleft between alpha-helical and beta-sheetrich domains and includes residues of aromatic cluster II. Uptake of ALA by monocytes proceeds at a slower rate in the presence of EGCG suggesting that EGCG binding may impair uptake of ALA by antigen-presenting cells. ALA, being of low cost and widely available protein, can serve as suitable delivery system for EGCG, as well as for food fortification with this bioactive catechin. (C) 2016 Elsevier Ltd. All rights reserved.